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Re: [RFC] TSC patch v2

From: Vesa Jääskeläinen
Subject: Re: [RFC] TSC patch v2
Date: Fri, 04 Jul 2008 23:48:30 +0300
User-agent: Thunderbird (Windows/20080421)

Colin D Bennett wrote:
On Fri, 04 Jul 2008 22:49:59 +0300
Vesa Jääskeläinen <address@hidden> wrote:

Hi Colin,

Colin D Bennett wrote:
Here is an updated version of the TSC patch.

I addressed the issues in your comments with the exception of
supporting x86 CPUs that don't have a TSC (386 and 486).

I eliminated the grub_time_init() function and the call to it in
grub_main() in favor of having grub_machine_init() simply call
grub_tsc_calibrate().  The i386-pc and i386-efi platforms use the
Please still use grub_time_init(). Detect TSC, if it is there
calibrate and adapt for it. If it is not there, use RTC.

Should grub_time_init() be a CPU or machine independent function?
Should it use conditional compilation to be usable on different CPUs?
Or should grub_time_init() be specific to i386 kernels at this point?
(Since we don't have anything to initialize for non-TSC-supporting

In your patch you just change call of grub_tsc_calibrate() to grub_time_init(). And in grub_time_init() you check cpuflags if tsc is available or not. If tsc is available you call grub_tsc_calibrate(). And if you are planning to use function pointers then you set proper function pointers accordingly.

If grub_time_init() is specific to the i386 CPU, then grub_time_init()
should check whether the CPU has TSC support, and if so,
grub_tsc_calibrate() should be called, and calls to grub_get_time_ms()
should be directed to the TSC implementation.  If no TSC support is
available, then no calibration is done, and calls to grub_get_time_ms()
should be directed to the generic get_time_ms() implementation that
uses grub_get_rtc() to do its job.

You can even make it something like:

- check for cpu flags (eg. detect method)
- if tsc, set function pointers rtc (init=tsc, getters=tsc)
- if no tsc set function pointers to rtc (init=rtc, getters=rtc)
- call function pointer init

I want to make sure that I clearly understand what you want, since I
have made major re-designs of the TSC support in GRUB in an attempt to
do what you want.  Just in the past couple of days I have spent about 8
hours getting the TSC patch where it is now. (I know that seems
like a lot since it's not that much code, but I am just beginning to get
familiar with the GRUB kernel organization, so simple changes have been
taking me a long time.)

Sure... This is why it is good to discuss and design these things on mailing list :)

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